Two stage heavy oil coking process



July 5, 1960, 'r. s. MERTES TWO STAGE HEAVY on. coxmc PROCESS Filed April 15, 1958 we m r 0 MM a m a 3 H 7M 9 m 0 a S G 3 EQZQM 85 9.8 3 2 2x8 NN H H W aw x mm L 9 #3 I a r 1 8 r r w m m m m m w w. u 0 mm m N M m. w w .l f 0 w m 8 m m m H n .H .O Om C P P .w .J owl 2m 26 5 on w 28 8E MMUS 62 80 E 9 mm 9. o.

INVENTOR. THOMAS S. MERTES BY 9 119/ R MO A 'l aQNEY EE- n n TWO STAGE HEAVY OIL COKING PROCESS Thomas S. Mertes, Wilmington, DeL, assignor to Sun glil Company, Philadelphia, Pa., a corporation of New ersey Filed Apr. 15, 1958, Ser. No. 728,685 Claims. ((11.208-53) This invention relates to a method for converting heavy hydrocarbon oils, and the like, and more particularly to a method for obtaining higher quality gasoline, gas oil, and lighter fractions from the coking of such heavy hydrocarbon oils.

The fluid coking process is known to be an elficient method for conversion of such heavy hydrocarbon oil feeds as heavy or reduced crudes, vacuum bottoms, pitch, asphalt, and other heavy hydrocarbon residua, or mixtures thereof. The fluid coking unit consists basically of a reaction vessel or coker where the coking takes place, and a burner where the circulating fluid coke is heated by partial combustion before being returned to the coker. In the coker the heavy oil to be processed is contacted with a dense, turbulent fluidized bed of the hot coke particles. Uniform temperatures exist in the coking bed. Uniform mixing in the bed distributes the feed stock throughout the bed and results in substantially isothermal conditions. In the coker the feed stock is vaporized and partially cracked. Product vapors are removed from the coker and sent to a fractionator for the recovery of gas, gasoline and light distillates therefrom. Gas oil from the fractionation is used as charge stock for catalytic cracking. The coke produced in the process is deposited on the circulated coke, and is circu- .lated to the burner, where it is subjected to partial comtbustion and recycled. A portion of the coke is continuously removed from the process as product.

Many of the crudes now processed contain large amounts of sulfur. Often the material fed to the coker in the fluid coking process contains 3% to 4% or more sulfur. A large proportion of this sulfur is carried over with the vaporous products, and remains as a contamimant in the gas oil produced. Such high sulfur con- .tent causes rapid deterioration of the catalyst in subsequent catalytic cracking operations, and is therefore 'undesirable. In addition, the gas oil contains large proportions of polycyclic aromatics, which reduce the effi- -.ciency of catalytic cracking.

It is therefore an object of this invention to provide -.a new method for conversion of heavy hydrocarbon oils. It is another object to provide a method whereby a highly .superior feed stock for catalytic cracking may be ob- .tained from heavy hydrocarbon oils having a high sulfur content. Still another object is to provide a method for separating a substantial proportion of the sulfur from .the gas oil produced by the coking of heavy hydrocarbon oils.

These and other objects are attained, according to the process of this invention, by coking a heavy hydrocarbon oil, whereby vaporous conversion products are produced, separating a gas oil fraction from the vaporous conversion products, extracting substantially all of the aromaticportion of said gas oil fraction, and coking the aromatic portion under conditions substantially more :severe than those of the first coking, whereby additional vaporous conversion products are produced.

In a preferred embodiment of the invention, the additional vaporous conversion products are recycled to the first coking step, so that these conversion products assist in the heating of the heavy hydrocarbon oil feed stock.

By the process of this invention higher proportions of gasoline and lighter fractions are produced,- at the expense of lower proportions of gas oil. However, the

rafi'inate from the extraction has a much lower proper} tion of sulfur, nitrogen, and other contaminants so that a highly superior charge stock for catalytic cracking is obtained. Catalyst poisoning is greatly reduced, and the need for expensive treatment, such as hydrogenation, in order to remove sulfur compounds, is eliminated. In addition, the charge stock to the catalytic cracker is substantially completely parafiinic, thus greatly facilitating the cracking operation.

In both coking steps, a substantial proportion of the sulfur in the feed stock and in the extract from the extraction is deposited on the coke, and a large proportion of this is burned ofi when the coke is subjected to partial combustion in the burner.

For a better understanding of the invention, reference is now made to the attached drawing, which is a flow diagram of the process of the invention.

Heavy hydrocarbon oil feed material is introduced through line 10 to primary coker 12, where it contacts a fluidized hot coke at a temperature of about 950 F. This contacting results in the formation of additional coke which, together with the contact coke, is circulated through line 14 to primary burner 16. In the burner, the coke is heated to about 1100 F. by partial combustion, air being introduced at 13 to support combustion. Flue gases are drawn off at 20. The heated coke is then returned to the primary coker through line 22 to maintain the 950 F. temperature therein. A portion of the coke withdrawn from the primary coker through line 14 is taken off as product at 24 in order to maintain the desired amount of coke in the system.

Vaporous conversion products from the primary coker, including dry gas, propane, butane, olefins, gasoline, and gas ,oil, are removed through line 26 and fractionated at 28. Gasoline and lighter fractions are taken olf overhead at 30, and the gas oil fraction passed through line 32 to extraction chamber 34, where it is subjected to counterflow extraction by a solvent, such as furfural, Cellosolve, nitrobenzene, or acetonitrile, which is selective to aromatics. The solvent is introduced through line 36. The raflinate, primarily paraifinic materials containing a small porportion of the solvent, is drawn off overhead at 42, and after fractionating to remove the solvent, is suitable for catalytic cracking without further treatment.

The aromatic-rich extract is drawn from the extraction chamber 34- through line 44 and introduced to a fractionator at 46, where the solvent is taken ofi overhead and returned to the extraction chamber via line 36. The aromatic-rich extract oil is withdrawn 'through'line 48 and introduced into a secondary coker at '50, where it is contacted with hot coke at about'llOO" F. This hot coke has been obtained by taking a' drag stream from primary burner 16 and introducing it to a secondary burner 52 through line 54. Here the 'coke is heated, by partial combustion, to a temperature of from'aboiit 1200 F. to about 1800 F. Air for combustion is supplied at 56, and flue gases are taken ed at 58. The

heated coke is then introduced to the secondary coker 50 through line 66, to maintain the desired temperature range therein. 7

On contacting the hot coke, the extract which is introduced into the secondary reactor is vaporized and partially cracked, with the formation of additional coke.

Patented July 5, 1960 Coke-from the secondary coker is passed, through line passed through line 66 and 26 to fractionator 28. Valves 68 and .70 in lines 64'and66, respectively, provide means for directing the flow of these vaporous conversion products- As is quite customary in :handling hot ivapors,

coolingmay be provided by recirculating a cooled gas oiLstreamto serveasaquench for the vapors entering the fractionator,,28. I

v;'The coke is heated in the primary .burner to a temperature'of from about 1000 F. tofabout 1200 F., the exact temperature. selected being determined by the amount of heat necessary to maintain the desired temperaturein the primary coker. .Theprima'r-y coker gives best results at an operating temperature :of about 950 F., although temperatures of from about 900. F. to about 1000..F. will;give goodresults; J

Solvent extraction is well known in theart, and it is not necessary. 'here to. described in detail thatportion of the ..process.' Generally temperatures of about.70 .F.

' to 150 F.- are used, and about 0.25 to about 5.0 volumes of solvent. are used per volume of gas oil. Instead of solvent extraction, other methods of separating aromatics from parafiinic materials, such as adsorption-desorption,

maybeuse'd.v V

In thesecondary burner, .the .coke is heated to a temperature substantially higher than that obtained in the primary burner. Temperatures of about. 1200 F. to about -1800? F. are used with goodresults. Such temperatures result in the burning ofi of substantial quantities of sulfur from the coke in the burner. This coke is ,then .passed tothe secondary coker, where it is used to .maintain the. desired temperature therein. .Preferably, the temperature in the secondary coker.is from 100 F. to 500 F. higher than thatin .the primary coker, thereby providing cracking of the extract from the solvent extraction under conditions substantially more severe than those prevailing in the primary coker.v Temperatures of from about 1050 F. to about 1500 F. are used with good results.

.The process of this invention is highly beneficial in the refining of any heavy hydrocarbonv feed, .since greater proportions of gasoline and lower boiling fractions are produced by this process than by processes previously used. Inaddition, a better feed material for catalytic cracking is obtained, since substantially all aromatics are eliminated. Where the heavy hydrocarbon feed materialhas a high sulfur content, still. other. benefits are obtained, in that the raflinate from the solvent extraction has a substantially lower sulfur content when the process of the present invention is used. Heretofore it has often been necessary to hydrogenate the charge material to the catalytic cracker in order to reduce the sulfur content when high sulfur crudes are processed. In the present process, a major proportion of the sulfur in the gas oil from the primary coker is extracted in the solvent extraction process, so that the sulfur remaining in the rafiinate is reduced to a low level. Even when the sulfur content of the heavy hydrocarbon feed material is as high as 4%, the process of this invention will produce a catalytic cracker feed stock having a sulfur content below about 1.5%.

The following example illustrates the process of this invention andthe advantages obtained thereby.

Approximately 10,000 bbls./ day of fresh residuum having a sulfur content of 3% is introduced into a fluid coker maintained at a uniform temperature'of about 950 F. vaporous conversion products from the coker C (butane, etc.) 7 rln are fractionated, the gasoline and higher boiling fractions being taken ofi overhead and the gas oil. bottoms being transferred to storage for catalytic cracking feed material. Products obtained are as follows, the gas being expressed as fuel oil equivalent.

The gas oil contains about 2.5% sulfur and aboritfi of aromatics.

the 'furfural removed, and-'theextr ac t oil, ar s-erase bbls./ day, is ir'itrodueed into a secondary coker mam tained at a tem'perature of 1100 F. The temperature in the secondary coker is maintained by introducingcoke from a secondary burner, whereit is heated to about 1350" F. Feed coke for the secondary burner istakenfrom the primary coking system. va orous eonversion products from the secondary coker are recycled to the primary coker. follows: Gas .bbls'./:day' l C (propane, etc.) 'do i C (butane, etc.) c lo Q2510 Gasoline do' 2520 i 3. 9 Net .coke e ,i 313 The sulfur content of the gas oil produced i's-l1'.-4% and contains substantially no aromatics. itisse'eH that although a lesser amount of gas oil'is obtained, the

gasoline yield is higher, and the gas oil is'a much better.

feed material for catalytic cracking, and consequently the catalytic cracking process will be more eificient with considerably less fouling of catalyst, and willproducea higher quality product. The overall volume of gasoline product, including that produced in catalytic cracking, is at least equal to that which can. be produced without the solvent extraction and recycling. In addition, "gas oil produced by catalytic cracking is a significantly better stock for blending to #2 fuel oil, due to its lower sulfur content. a

The invention'claimed is: V 1. A hydrocarbon conversion'proces's which comprises coking a heavy hydrocarbon oil, whereby vaporous con version products are produced, separating a gas oil fraction from the vaporous conversion products, extracting substantially all of the aromatic portion of said :gas oil fraction, and coking said aromatic portion under conditions substantially more severe than those of the first coking, whereby additional vaporous conversion products are produced.

2. A hydrocarbon conversion process which comprises coking a heavy hydrocarbon oil, whereby vaporous conversion products are produced, separating a gas oil fraction from the vaporous conversion products, extracting substantially all of the aromatic portion ofsaid gas oil fraction, coking said aromatic portion at a temperature from about F. to about 500 F. higher than the temperature of the first coking, whereby additional vapor.- cus conversion products are produced, andrecycling said additional vaporous conversion products to the first coking step. a

3. A hydrocarbon conversion process whnn'con srisa coking a heavy hydrocarbon oil containing sulfur, at a temperature of from about 900 F. to about 1000 F.,

whereby vaporous conversion products are produced;

Product yield from-this rocess is as separating a gas oil fraction from the vaporous conversion products, extracting substantially all of the aromatic portion of said gas oil fraction, together with a major proportion of the sulfur in said gas oil fraction, and coking the extract from said extracting at a temperature of from about 1050 F. to about 1500 F., whereby additional vaporous conversion products are produced.

4. A hydrocarbon conversion process which comprises heating and cracking a heavy hydrocarbon oil in a coker at a temperature of from about 900 F. to about 1000 F., whereby vaporous conversion products are produced, recovering a gas oil fraction from said vaporous conversion products, solvent extracting said gas oil fraction to produce a primarily paraflinic rafiinate phase and an aromatic-rich extract phase, separating solvent from said extract phase to produce an aromatic-rich extract oil, and heating and cracking said extract oil in a coker at a temperature of from about 1050" F. to about 1500 F., whereby additional conversion products are produced.

5. A process for coking heavy petroleum fractions which comprises contacting, in a first coking zone, a heavy petroleum fraction with a fluidized bed of coke at a temperature of from 9001 F. to 1100" F., recovering cracked products from the first coking zone, separating a. gas oil fraction from the cracked products, fractionating the gas oil fraction into a relatively paratfinic fraction and a relatiWely aromatic fraction, contacting the relatively aromatic fraction, in a second coking zone, with a fluidized bed of coke at a temperature of from 1000 F. to 1600 F., the temperature in said second coking zone being at least 100 F. higher than in the first coking zone, recovering coke from said second coking zone at a temperature higher than the temperature in said first coking zone, and passing the so-recovered coke to the first coking zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,727,853 Hennig Dec. 20, 1955 20 2,777,802 Peet Jan. 15, 1957 2,847,357 Moser Aug. 12, 1958 

1. A HYDROCARBON CONVERSION PROCESS WHICH COMPRISES COKING A HEAVY HYDROCARBON OIL, WHERBY VAPOROUS CONVISION PRODUCTS ARE PRODUCED, SEPARATING A GAS OIL FRACTION FROM THE VAPOROUS CONVERSION PRODUCTS, EXTRACTING SUBSTANTIALLY ALL OF THE AROMATIC PORTION OF SAID GAS OIL FRACTION, AND COKING SAID AROMATIC PORTION UNDER CONDITIONS SUBSTANTIALLY MORE SEVERE THAN THOSE OF THE FIRST COKING, WHERBY ADDITIONAL VAPOROUS CONVERSION PRODUCTS ARE PRODUCED. 